Dentist told me to take amox 500 tid, I have a huge bottle from march left over and it dawned on me it says discard 3/24, is it still safe to take?

Yes & no. It is safe to take in that it won't cause you harm. However, the efficacy/potency may have faded such that it won't give you the intended therapeutic benefit at the dose needed. This can be problematic because the bacteria could develop a resistance to it. If it's expired, discard it in the trash or local prescription waste collection depot. Don't flush it down the toilet.
Take it. The bottle says expires 2013, which means it is still potent. Some state pharmacy laws indicate that the expiration date on the orange tube that pills are dispensed in have an expiration date one year from the fill date. But the original bottle expiration might be longer (this is obvious in eyedrops). Most drugs expire well after the expiration date.
Discard. That is the standard piece of advice. In fact, the margin of safety is such that in all probability the medication is entirely safe to use. If you want to be a stickler about it, then get rid of it and buy more.